1. Field of the Invention
The invention concerns a traffic control system and the use of such a system in connection with train traffic. The invention moreover concerns a method of controlling the movement of a mobile unit.
2. Description of the Related Art
The work on increasing train speeds has created a need for ensuring reliable train control systems.
EP-A-145 464 discloses a train control system wherein transponders, applying a coded response to an inquiry, are located along the track. A train receives information on the code of the next transponder from a control centre, and the train reports when this code has been detected. If the transponder is not detected, the train is brought to a standstill.
GB-A-2 219 833 discloses a traffic information system for use in bus traffic. A transmitter is provided at each bus stop, transmitting a code to a bus when interrogated, whereby the position of the bus may be determined. This information may be used e.g. in traffic control centres for putting on more buses if necessary.
U.S. Pat No. 5,129,605 discloses a system wherein a plurality of different position determination systems are used for determining the exact position of a train. The whole is controlled by a control centre which coordinates the information.
Furthermore, a safety system called automatic train control (ATC) has been developed for the purpose of improving train safety. This system protects against a number of human errors on the part of the train drivers, one of the basics of the system being that the train is provided with a computer which receives traffic information, such as stop signals and speed limits, from a plurality of transmitters along the track. Thus, the computer may bring the train to a standstill irrespective of what the train driver does when the train arrives at a stop signal. The signals and the transmitters are controlled from a central signalling post.
Finally, U.S. Pat. No. 3,940,765 discloses a traffic control system for trains, having a plurality of stationary passive units. This known system does not enable the trains to transmit messages to the stationary units.
The object of the invention is to provide a system making it possible to control a mobile unit, such as a train, which can take place without interference from a traffic control centre as long as the flow of traffic is smooth.
This object is achieved in that the traffic control system is provided with the constructive features of the present invention. The use of stationary, passive units arranged along a track obviates the need for running cables along the track. Thus, it is easy to encapsulate the stationary units so as to avoid ingress of water. The system is thus extremely insensitive to wind and weather. The stationary units apply a unique code to an interrogation, and the computer of a mobile unit can determine its position, the positions of the stationary units, following mounting, being determined exactly and stored electronically. The mobile unit can hereby determine its position on the basis of the unique code by an electronic look-up table. The mobile unit simultaneously receives traffic information, such as speed limits and data concerning the last-passed mobile unit, such as a train on the point concerned of the section, which supplies these data to the stationary units. It is hereby possible to control the speed pilot of the train by data obtained directly from the stationary unit. As mentioned, the traffic information may also include information concerning the last-passed train, it being hereby possible to estimate the distance to the preceding train and to determine the distance to it. The movement of the train or the mobile unit may thus be adjusted according to this information. This train control may be made additionally safe in that the trains automatically transmit the message to a central control unit, if they no longer keep an expected timetable, so that subsequent trains can calculate more safely whether the section ahead is unoccupied by combining data obtained from the stationary units with data concerning anomaly for a train ahead.
Expediently, the stationary units are tags which transmit and receive at frequencies, preferably at 27 MHz. The tags may hereby be buried and thus concealed and protected against wind and weather.
The stationary units are constructed to produce a very inexpensive and practically maintenance-free traffic control system, because the circuits are powered by the electromagnetic energy released by the mobile units through their interrogation signal.
Traffic messages may consist of the interrogation time of the mobile unit and identity information concerning the mobile unit. These data are communicated to the next unit and are then erased, since they are no longer of interest. The traffic messages may comprise speed limits and information on local conditions, and this information may be a warning of work along the track, etc.
The calculated position information may be displayed on a display, the information being represented either by numerical values or as a graphic indication on a map.
The control unit of the mobile unit calculates the distance to the last-passed mobile unit--optionally in time--which takes place on the basis of the received traffic messages from the stationary units and optionally from a traffic control centre if the last-passed unit does not keep a predetermined timetable.
Storage of driving-technical information expediently takes place while more permanent traffic messages are stored after the completion of a successful recognition procedure, i.e. a mobile unit is to validate that it is entitled to store the type of messages concerned, and such a procedure is usually called a handshaking procedure. Corresponding procedures are performed when such permanent traffic messages are erased.
The traffic control system may be used in connection with a large number of mobile units, and these follow a more or less predetermined route. This may e.g. be taxiing of aircraft in airports, where the pilot himself can taxi the aircraft to a gate, and the control tower does not have to interfere as long as there is no other aircraft along the route concerned. The system can be used in connection with public bus traffic, since a computer incorporated in a bus can transmit information to a traffic control centre if the bus does not keep the timetable. The traffic control centre can then display the expected changed arrivals at subsequent bus stops. The passengers will hereby be kept currently informed of the expected arrival of the next bus. However, the system finds particular application within traffic control systems in connection with railway traffic. Here, the train driver can drive the train without interference from the traffic control center as long as the established timetable is kept. The train drivers are no longer referred to visual signals along the track, but can drive the train on the basis of their knowledge of the position of the train and the knowledge of the position of the last-passed train. This opens up the prospect of introducing driver-less trains, where the computer of the train controls its movements.
The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawing, in which: